Damped cavity for linear collider

In order to increase the luminosity of a linear collider, we adopt multi-bunch operation. In this case, higher order modes excited in an accelerating structure by the preceding bunches in a bunch train are likely to cause beam breakup in the following bunches. As a method to suppress this effect, we studied a cavity whose Q values are damped enough for the higher order modes. In this paper, we first explain the damping method and then we show the field calculations using a 3D code MAFIA to try to make the Q values less than 20 without decreasing the Q value of the fundamental mode. Finally, we describe results of low power measurements for a test cavity. The Q value of the TM110 π-mode was found to be decreased to 10. (author)